The difference spectrum obtained by subtracting a low power EPR signal from a high power EPR signal of the copper enzyme nitrous oxide reductase (N2OR) is assigned to a mixed valence [Cu(1.5+)...Cu(1.5+)] signal. The relaxation of the signal is much faster than the relaxation of the binuclear mixed valence [CuA(1.5+)...CuA(1.5+)] signal from the electron transfer site in N2OR. It is suggested that this signal is a modified form of the mixed valence [CuA(1.5+)...CuA(1.5+)] electron transfer site.